The params represent specific parameters we need to recreate the
connection to the database in the event of a failure. If they're not set
then recovery is out of our control.
Could also use it to pass other information, such as the readonly flag.

For commit_one_phase we can do whatever we want since the transaction
outcome is whatever we want. Therefore, we do not need to save any
additional recoverable state, such as a reference to the transaction
coordinator, since it will not have an intentions list anyway.